Document imaging is well known in the art. When scanning documents of value such as for example cheques, ensuring that the resultant document images are of sufficient quality for subsequent processing is important. Various techniques for assuring image quality have been considered.
For example, U.S. Pat. No. 6,912,297 and U.S. Patent Application Publication No. 2005/0175221 to Scott et al. disclose a method of determining whether a cheque document in an image has a torn or folded corner. A tracing algorithm is used to trace along a diagonal line of pixels from a corner of the cheque document within the image. If the pixel located in the expected position of the corner of the cheque document does not represent part of the cheque document, the pixels along the diagonal line are checked in succession. If pixels representing part of the cheque document are found along the diagonal line, the path of the diagonal line is deviated and pixels along the deviated diagonal line are checked in succession to determine if they represent part of the cheque document. If the number of consecutive pixels along the deviated diagonal path that do not represent the cheque document exceeds a threshold, a tear or fold is deemed to be present. In order to distinguish between folds and tears, the first pixel representing part of the cheque document is located along both sides of the expected edges of the cheque document from the corner. A straight line is determined between these two pixels, and pixels adjacent this straight line along each row or column are checked to determine if the missing portion of the cheque document represents a fold or a tear.
U.S. Pat. No. 5,754,674 to Ott et al. discloses a method and system for determining whether a cheque image is acceptable. A first normal sensitivity image and a second more intense sensitivity image of a cheque are captured. Speckle filtering is performed on both cheque images. Clusters of black pixels are grouped and classified as stroke-like or otherwise based on a number of statistics. If a cluster of black pixels in the first cheque image is classified as stroke-like, but is not recognized, the second cheque image is analyzed to determine if the particular cluster of black pixels forms part of another cluster of black pixels.
U.S. Pat. No. 5,870,508 to Park discloses a method of aligning a document image using horizontal and vertical alignment lines placed on a document in the image. The alignment lines are located in the document image, and one or more translations required to translate the document in the image into a correctly-aligned orientation are determined using the alignment lines. The document image is then oriented using the determined translations.
U.S. Pat. No. 5,901,253 to Tretter discloses a method of determining the skew angle of a document image. The edge of the document in the image is determined by comparing each line scanned with that of a background when the document is not present. The first and last pixels forming part of the document in each scan line are registered and collectively form the edge. The slope of the detected edge is then determined and used to calculate the orientation of the document in the image.
U.S. Pat. No. 6,310,984 and U.S. Patent Application Publication No. 2001/0014183 to Sansom-Wai et al. disclose a system and method for automatically determining the presence of extraneous information in a cheque image. The extraneous information is then ignored to determine the skew of the cheque document in the image.
U.S. Pat. No. 6,587,576 to Wesolkowski discloses a method of determining the quality of a grayscale cheque image. A two-dimensional histogram of the cheque image is generated using the grayscale values of the pixels in the cheque image. One axis of the histogram represents the foreground or actual grayscale values of the pixels. The other axis of the histogram represents the background values of the pixels, calculated as the average grayscale value of a surrounding N×N pixel window. The centers of background and foreground pixel clusters are determined and the normalized distance therebetween is calculated. This distance is used to determine the quality of the cheque image.
Although the above references disclose techniques for evaluating the quality of document images, improvements to assure image quality are desired. It is therefore an object of the present invention to provide a novel method and apparatus for evaluating the quality of document images.